1. Field of Invention
This invention relates to a helical pipe, more particularly to a Bourdon's helical pipe incorporated in a hydraulically actuated weighting scale, the helical pipe of which has an air releasing means provided at its sealed end thereof.
2. Description of the Related Art
Scales are widely used for measuring the weight of objects or people. The general requirements for a scale are: application of the range of weight to be measured, accuracy in displaying the weight readings, linearity in responding to weight changes and simplicity in mechanical construction thereof. Various kinds of scales have been available in the past; a popular one is shown in FIG. 1 for measuring weight which uses a pressurized fluid means to actuate an indicating needle thereby to read a weight applied thereon. As shown, the scale is composed of a base member A, a top cover B, a gage D and a dial D1 for displaying the weight reading, an assembly of levers B2 and having four fulcrums B1 and a force exerting terminal B3 and a weight sensor C which is usually made of a spring assembly with said force exerting terminal B3 arrested thereon, and a oil pump E with a first pipe E1 connected to said gage D and second pipe E2 connected to said weight sensor C. It is known that the weight sensor C actually serves as an intermediate means for transferring the sensed pressure to the pressure gage D. In this scale, a Bourdon's pipe is used as an intermediate transmission apparatus to sense the applied weight.
FIG. 2 shows the scale of FIG. 1 with the top cover B removed. As illustrated, the Bourdon's pipe F2 is in the shape of a "C", an oval cross-section through which pressurized fluid from a fluid inlet F11 can flow. When the pressure inside the pipe F2 is increased, the oval pipe F2 tends to become circular and this causes the pipe F2 to straighten. The sealed inner end portion F21 of the pipe F2 will impel an end of a connected rod F3. The other end of the connecting rod F3 in turn rotates a sector gear F5 about a pivot pin F14 so that an indicating needle F61 is rotated by meshing the teeth of the sector gear F5 with a gear shaft F7 on which the indicating needle F61 is mounted so as to indicate an applied weight on the dial. When the applied weight is removed, the indicating needle F61 is pushed back to the original position by a torsion spring F8 having one end connected to said indicating needle F61 and the other end connected to a support F9, whereat the needle rests to point "0" on the dial D1.
It has been found that the hydraulically actuated scale which uses a helical pipe as a weight transmission apparatus that can measure an object or a person only within a limited range. The above-mentioned scale can not be accurately used to measure a weight outside of the limited range, because a pressurized fluid is compressed into the open end of Bourdon's helical pipe, some air is trapped within the sealed end of the same. Under this condition, the Bourdon pipe can sense a weight within a certain limited range. There is only one way to change the corresponding weight range of the scale without altering its overall construction. That is to adjustably release the trapped air from the interior of the Bourdon's pipe thereby to adjust the weight range to be measured by the same scale.